The present invention relates to ultrasound imaging. In particular, ultrasound imaging using different sources of information for reducing clutter or artifacts and adding missing small blood vessels back to the grayscale image is provided.
Ultrasound images are typically generated in response to acoustic beams electronically steered in an azimuth dimension and mechanically focused in an elevation dimension. In general, the elevation beam width is an order of one magnitude wider than azimuthal beam width. The elevation beam width varies as a function of range and includes signals from within the entire beam width. Wider beam widths increase unwanted signal or noise. The elevation beam width artifact decreases the contrast and obscures real structures, such as small vessels, cysts and the heart apex. The elevation beam width may result in clutter or weak signals indicating tissue within a large vessel or pool of fluid, such as near vessel walls. This elevation fold-in artifact confuses pathology with clutter and results in small vessels being not visible.
Narrower elevation beam width is provided using 1.5 dimensional or 2-dimensional transducer arrays. A narrower elevation beam width provides, more likely identification of small structures and cleaner large vessel. However, 1.5 dimensional and 2-dimensional transducer arrays require complicated manufacturing processes, additional system hardware and it is a probe specific solution. These complications increase the overall cost of an ultrasound system.
To further distinguish fluid, such as blood, from tissue in radiology imaging, a Doppler image representing velocity or power is overlaid on the B-mode or gray-scale image. Doppler information is thresholded to determine the presence of flow or tissue at each pixel or image location. Where sufficient flow is identified, the Doppler information is displayed in color instead of the B-mode information.
Doppler imaging or color flow imaging introduces different artifacts, such as a color flash artifact. Breathing, heart beating, muscle movement or other movement causes false detection of flow. Even without flash artifact, a jagged vessel boundary or strong discontinuity is created by the binary flow decision. The color Doppler information is intrusive, resulting in removing, overriding or otherwise altering B-mode border or vessel boundary information. Generally, Doppler images have worse resolution than grayscale images.
As an alternative to the binary criteria for distinguishing between flow and tissue, flow and tissue information maybe blended. A transparent color map superimposes the flow information on a B-mode or tissue information. For example, a white value or other characteristic of the Doppler color is altered as a function of a B-mode signal associated with the interior of a vessel or other fluid region. Various functions maybe used for the blending, such as a function that emphasizes tissue for low values of Doppler signal and quickly transverses to emphasizing Doppler signals for a midrange of B-mode values and provides strong emphasis on color information for low B-mode values. However, tissue and fluid borders are not as clearly defined or as sharp as more conventional B imaging. Another combination provides for mapping Doppler power information to gray-scale values with the tissue information. Some clutter may be removed but the vessel or pathology boundary is jagged or otherwise undesirable. This blending of Color and grayscale pixel further obscures the border.
A combination of both Doppler and B-mode image signals may remove some artifacts in cardiac imaging. U.S. Pat. No. 5,961,460 to Guracar, et al. discloses combinations of B-mode and Doppler image signals for enhancing moving tissue, such as heart valves or heart walls, and suppressing or removing information associated with clutter and stationary tissue. A modulated, non-linear function of both the B-mode and Doppler image signals is provided by a look-up table structure.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below include methods and systems for ultrasonic B-mode imaging with different signals for artifact reduction and organ morphology enhancement. The B-mode image signals and Doppler image signals are combined using a modulated, non-linear function. The end results are displayed in grayscale or superimposed with other kind of image. Portions of the B-mode image signal associated with stationary tissue are intact while portions of the B-mode image signal associated with flow are substantially suppressed. The suppression is pixel-by-pixel and gradual rather than binary to avoid flash artifacts, such as providing an adaptive modulated, non-linear combination function. Doppler or flow image signals are less sensitive than tissue or B-mode signals to elevation beam width. Suppressing the B-mode image signal where flow exists better identifies small vessels that would otherwise be characterized as tissue. Small vessel or other small structure information associated with fluid is inserted within the gray-scale or B-mode image. Clutter within large vessels is more likely mapped to black or removed. The pathology is kept intact by not removing stationary tissue information. The enhanced large vessel presentation and added visibility of small vessels provides more detail about tissue morphology for radiology applications. The resulting gray-scale image appears as if fine or narrow beams had been used in both the azimuth as well as the elevation directions. Unlike a true narrowing of the elevation beam at a focal point, the enhanced imaging is provided over an entire field of view.
In a first aspect, individual display indicia are provided as a modulated, non-linear function of both Doppler and B-mode image signals representing a same region. The non-linear function substantially enhances portions of the B-mode image signal associated with stationary tissue and substantially suppresses portions of the B-mode image signal associated with flow.
In a second aspect, one of a processor or dedicated mixing circuit is provided for implementing a modulated, non-linear function. The outputs from B-mode and Doppler detectors are provided for combination by the processor or mixing circuitry.
In a third aspect, individual display indicia are generated representing a modulated, non-linear function of both Doppler and B-mode signals. The nonlinear function modulates one of the B-mode and Doppler image signals with a weighted other one of the Doppler and B-mode signals. For example, a B-mode signal is modulated with a Doppler signal. Conversely, a Doppler signal is modulated by the B-mode signal.
In a fourth aspect, individual display indicia are generated representing an imaged region as a function of both Doppler and B-mode signals. One of the Doppler and B-mode image signals is modulated by the same Doppler or B-mode image signal. For example, a Doppler signal is modulated by a weight or other variable adaptively responsive to the Doppler signal. In another example, a B-mode image signal is modulated by a weight adaptively responsive to the B-mode image signal.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.